Honeybees are one of the most beneficial organisms in contemporary agriculture and they provide various products such as royal jelly, honey, propolis, and pollens, which serve as nutrition sources for human beings (Hellner M et al., 2008). Therefore, there have been great interests in the growth, evolution, and development of honey bees.
Honeybees live in matrilineal societies, and a bee colony is led by the queen bee. In a bee colony, worker bees and the queen bee are developed from fertilized eggs while drones are developed from unfertilized eggs (Winston M. L., 1987). The queen lays eggs singly in cells of the comb. Larvae hatch from eggs in three to four days. They are then fed by young worker bees and develop through several stages in the cells. Cells are capped by worker bees when the larva pupates. Queens emerge from their cells in 16 days, workers in 21 days and drones in 24 days. Queens are bigger in body size, and their lifespan is normally 10 to 15 times that of worker bees. Whether a fertilized egg develops into a worker bee or a queen is regulated by the bee colony. In principle, only one queen is present in a bee colony. Besides, a queen bee is fed differently from other bees in the same colony. The queen bee is fed royal jelly throughout its life, and worker bees are only fed royal jelly at the beginning of their development. While some researchers believe that worker bees are also fed royal jelly throughout their developmental stage, the royal jelly fed to worker bees may have different chemical constituents from that fed to the queen. In any case, royal jelly serves as the most important substance in maintenance of a bee colony (Robinson G. E. et al., 1987).
Royal jelly is the most important food and nutrition source for larvae of the queen bee and the queen. It is secreted by the hypopharyngeal and mandibular glands of young worker bees and the constituents of royal jelly may change at the different developmental stages of the larvae. In general, such change is considered to be reflected in the sugars rather than protein components of royal jelly (Peiren N. et al., 2005).
It is known that royal jelly comprises many substances capable of improving human health and has various pharmacological properties (Takaki-Doi S. et al., 2009; Mannoor M. K. et al., 2009; and Gasic S. et al., 2007). Therefore, royal jelly has been widely used in health food intended to promote human health. Recently, researches demonstrated that royal jelly is capable of promoting immune regulations (Vuecvic D. et al., 2007), exhibiting anti-bacterial functions (Boukraa L., 2008), nourishing cerebral nerves (Hashimoto M. et al., 2005), exhibiting anti-cancer and antioxidant activities (Guo H. et al., 2008). It has been found that royal jelly, which is opal thick liquid, is around 60-70% water, 12-15% proteins, 10-12% sugars, 3-5% lipids, and many trace elements and minerals (Scarselli R. et al., 2005). Among the protein components, around 89-90% are water-soluble proteins, and the rest are water-insoluble proteins. In other words, most of the proteins contained in royal jelly are water-soluble.
The MRJP (major royal jelly proteins; MRJP) family (MRJP 1-9) is the major component among these water-soluble proteins (Schmitzová J. et al, 1998). Although these MRJP proteins have been analyzed for their amino acid sequences, their functions are still unclear.
MRJP1 was identified in the brain of bees, and is assumed to be responsible for bees' behaviors. It accounts for 44% of the water-soluble proteins in royal jelly, and is the most abundant isoform among the MRJP family proteins (Malecová B. et al., 2003). To date, MRJP3 has received most attention, and it is considered that this protein plays a role in immune regulation (Kohno K. et al., 2004). It has also been found that MRJP3 accounts for 12% of total water-soluble proteins in royal jelly, and is the second most abundant isoform among all MRJP proteins (MRJPs 1-9). MRJP3 is distinct due to its antiallergic and anti-inflammatory activities. The 60-70 kDa proteins are variants of MRJP3 protein which is the product of the highly polymorphic MRJP gene (Stefan Albert et al., 1999).
MRJPs provide abundant essential amino acids and other nutrient components (Furusawa T et al., 2008). As royal jelly is the only nutrition source for larvae of the queen bee and MRJPs are the most important proteins in royal jelly, there is a need to develop the royal jelly with specific components.